1. Field of the Invention
The present invention relates to a semiconductor device, more specifically, to a semiconductor device including an absorption layer including a multiple quantum well structure.
2. Description of the Related Art
In general, a semiconductor device serving as a photodiode can be produced by forming an absorption layer including a multiple quantum well structure formed of III-V compound semiconductors on a buffer layer formed of GaSb (gallium antimonide). In a case where the multiple quantum well structure is formed so as to include a stack of unit structures each including an InAs (indium arsenide) layer and a GaSb layer, the semiconductor device can be produced as a photodiode for mid-infrared light.
In this case of forming, on the buffer layer, an absorption layer including a multiple quantum well structure including a stack of the unit structures, a difference in lattice constant between GaSb and InAs causes tensile strain to be applied to the InAs layers within unit structures. In a multiple quantum well structure having a stack of a large number of the unit structures, the presence of tensile strain may cause lattice relaxation therein.
One measure having been suggested for avoiding the occurrence of lattice relaxation is to form, within unit structures, strain compensation layers to which compressive strain is applied (for example, refer to Huang et al., “InAs/GaSb type-II superlattice structures and photodiodes grown by metalorganic chemical vapor deposition”, APPLIED PHYSICS LETTERS 96 251107, 2010; and Zhang et al., “Improved surface and structural properties of InAs/GaSb superlattices on (001) GaSb substrate by introducing an InAsSb layer at interfaces”, APPLIED PHYSICS LETTERS 90 131110, 2007).